Cataract extraction and intraocular lens insertion may be regarded as one of the most successful human body part replacement procedures ever developed. It has been said that “cataract surgery, the most successful procedure in modern medicine, yields outcomes that are unsurpassed by any other surgical procedure” (Obstbaum S. A. “Effective cataract surgery—an undervalued procedure”, J Cataract Refract Surg. 1998;24: 1417).
The deformable intracoular lens (IOL) was developed in the early 1980s. Formed of polymeric material, IOLs are sufficiently soft and flexible to allow the lens to be folded for insertion into the eye through an incision of reduced size.
IOLs typically incorporate a disk-shaped, transparent lens optic and may include smoothly curved attachment arms referred to as haptics. The lens optic typically is formed of polymeric material such as polymethyl methacrylate, virgin silicon or acrylic based materials, which are suitable for lathe turning or by moulding by injection, compression or cast moulding techniques.
IOL design developments over the years include: square edges to minimise posterior capsular opacity when the IOL is inserted into the posterior capsule of the eye during cataract surgery (Nagata T, Watanabe I. “Optic sharp edge or convexity: comparison of effects on posterior capsular opacification”, Jpn J Ophthalmol, 1996;40:397–403; Nishi O. et al “Inhibition of migrating lens epithelial cells at the capsular bend created by the rectangular optic edge of a posterior chamber intraocular lens” Ophthalmic Surg Lasers, 1998;29:587–94; Nishi O. et al “Preventing posterior capsule opacification by creating a discontinuous sharp bend in the capsule” J Cataract Refract Surg., 1999;25:521–6.); textured or frosted haptics to increase friction in the interface between tissue and the haptic portions so as to anchor the IOL in the eye (U.S. Pat. No. 6,129,759); and differential anterior and posterior coloration of haptics to facilitate lens orientation for insertion into the eye (U.S. Pat. No. 6,325,055).
Notwithstanding the tremendous developments in cataract treatment, including IOL design, visual disturbances are reported by patients which include glare, streaks and/or dark shadows in the temporal visual field (Nadler D. J, et al “Glare disability in eyes with intraocular lenses” Am J Ophthalmol 1984;97:43–47; Masket S. et al “Undesired light images associated with ovoid intraocular lenses” J Cataract Ref Surg 1999;19:690–694; Tester R. et al “Dysphotopsia in phakic and pseudophakic patients: incidence and relation to intraocular lens type” J Cataract Ref Surg 2000;26:810–816; Häring G. et al “Subjective photic phenomena with refractive multifocal and monofocal intraocular lenses” J Cataract Ref Surg 2001;27:245–249; Davidson J. A. “Positive and negative dysphotopsia in patients with acrylic intraocular lenses” J Cataract Ref Surg 2000;26:1346–1355. These visual disturbances may be referred to as “photic disturbances”. In the pseudophakic human eye in particular (where the crystalline lens has been surgically removed) photic disturbances (termed pseudophakic dysphotopsia—Tester R. et al in phakic and pseudophakic patients: incidence and relation to intraocular lens type” J Cataract Ref Surg 2000;26:810–816) can adversely impact the quality of vision and may affect 7–90% of patients implanted with intraocular lenses (Häring G. et al “Subjective photic phenomena with refractive multifocal and monofocal intraocular lenses” J Cataract Ref Surg 2001;27:245–249; Meacock W. R. et al “The effect of texturing the intraocular lens edge on postoperative glare symptoms. A randomized, prospective, double-masked study” Arch Ophthalmol 2002;120:1294–1298.)
Unwanted image formation is a troublesome problem in the pseudophakic eye after IOL insertion. Holliday (Holladay J. T. et al “Analysis of edge glare phenomenon in intraocular lens designs” J Cataract Ref Surg 1999;25:748–752) using ray tracing techniques has investigated the edge glare effects in IOLs. Holliday concluded that rounded edges of the IOL reduce edge glare phenomenon. However, edge glare remains a problem in these conventional designs (Masket S. et al “Undesired light images associated with ovoid intraocular lenses” J Cataract Ref Surg 1999; 19:690–694; Tester R. et al “Dysphotopsia in phakic and pseudophakic patients: incidence and relation to intraocular lens type” J Cataract Ref Surg 2000;26:810–816; Davidson J. A. “Positive and negative dysphotopsia in patients with acrylic intraocular lenses” J Cataract Ref Surg 2000;26:1346–1355; Meacock W. R. et al “The effect of texturing the intraocular lens edge on postoperative glare symptoms. A randomized, prospective, double-masked study” Arch Ophthalmol 2002;120:1294–1298; Holladay J. T. et al “Analysis of edge glare phenomenon in intraocular lens designs” J Cataract Ref Surg 1999;25:748–752; Erie J. C. et al “Analysis of postoperative glare and intraocular lens design” J Cataract Ref Surg 2001;27:614–21; Masket S. “Truncated edge design, dysphotopsia, and inhibition of posterior capsule opacification” J Cataract Ref Surg 2000;26:145–147; Ellis M. F. “Sharp-edged intraocular lens design as a cause of permanent glare” J Cataract Ref Surg 2001;27:1061–1064; Kohnen T. “The squared, sharp-edged optic intraocular lens design” J Cataract Ref Surg 2001;27:485–486). Further, such rounded edge designs may be associated with an increased risk of posterior capsular opacification (Kruger A. J. et al “Two year results: sharp versus rounded optic edges on silicone lenses” J Cataract Refract Surg., 2000;26:566–70).
Photic disturbances may also occur in IOLs located outside of the lens capsule, for example for vision correction, with artificial corneas and contact lenses.
This invention is concerned with the problems of photic disturbances associated with ocular lenses, including IOLs, artificial corneas and contact lenses.